1. Field of the Invention
This invention relates to transaxles, especially a hydraulically operated semi-automatic planetary transaxle assembly.
2. Description of the Related Art
A semi-automatic transaxle comprises a differential section and a transmission section coupled to an engine with a torque converter. The transmission section contains hydraulically controlled clutches and bands. The transmission section includes a transmission fluid pump to create the requisite hydraulic pressure. This fluid pressure is regulated and directed, by a valve body assembly, to the clutches and bands in various combinations in order to provide several output gear ratios to the differential.
Numerous design features exist for transaxles.
The basic structure of a semi-automatic transaxle consists of an input shaft coming from a torque converter that is connected to the engine, an intermediate shaft, optional drop-down gears, an output or pinion shaft, a pinion gear, a ring gear, clutches, and bands.
In some transaxles, transmission fluid from the torque converter travels within a channel running longitudinally inside the input shaft to be used subsequently for lubrication. This is, however, not desirable because having the input shaft hollow structurally weakens the input shaft. In some other transaxles the transmission fluid travels along the surface of the input shaft before descending into a channel of the input shaft in order to travel further. Again this introduces structural weakness and is, therefore, undesirable.
Some transaxles place a transmission fluid pump on the front of the differential section of the transaxle, enabling the drop-down gears to be at the back of the transmission section of the transaxle.
In some transaxles, tapered roller bearings at the pinion gear and ring gear positions are provided with shims behind the bearing cups to allow more precise positioning.
The transmission fluid pump in some transaxles circulates transmission fluid to a cooler (such as a radiator or heat exchanger) in order to lower the temperature of transmission fluid coming from the torque converter, which is quite hot.
Billet 300M steel is utilized in the input shaft and the intermediate shaft of some transaxles in order to increase strength.
Clutch drums in some transaxles are machined from billet 300M steel in order to increase strength.
Hollow dowels are used in joining sections of some transaxles to provide precise centering and alignment.
For some transaxles, steel thread inserts line the cavity where a bolt is to be screwed into aluminum.
And in some transaxles, an oil pump provides oil to be sprayed on the ring and pinion gears as well as the drop-down gears in order to cool them. Such oil is collected in a reservoir below the transaxle and circulated through a cooler.
No transaxle is, however, known to the inventor which incorporates all of the preceding features other than the undesirable hollow input shaft.
And the only semi-automatic transaxle known by the inventor to be used in vehicles intended for off-road racing is an Audi transmission coupled with an after-market differential section designed for passenger cars having 150 to 200 horsepower.
In the Audi transaxle of FIGS. 1a and 1b, the input shaft 2 and the intermediate shaft 5 are hollow so that a smaller shaft 1 can pass through them to power the transmission fluid pump, which is located at the extreme rear of the transmission case. This hollow structure, as suggested above, weakens the input shaft 2 and the intermediate shaft 5, causing them to be prone to twisting and breaking.
Moreover, the flow of power in the Audi transaxle is, as depicted in FIG. 1b, rather complicated. As illustrated in FIG. 1b, the input shaft 2 goes through the differential section 3 to the transmission section 4 and proceeds inside the intermediate shaft 5. When the clutch 6 is engaged, the intermediate shaft 5 sends the power back toward the differential section 3 to the drop-down gears 7 to reach the output shaft 8 in the differential section 3.
Additionally, the Audi clutch drums are made of a cast material of limited strength; and the differential section, being an after-market unit designed to be compatible with the Audi transmission unit, is similarly of limited strength.
There is no provision in the Audi transaxle for adjustments to the location of ring gear and pinion gear in order to achieve a wear pattern that will yield long life and reliability. Nor does the Audi transaxle provide for cooling the differential gear oil.
And two final disadvantage of the Audi transaxle are (a) that it does not have alignment dowels where the differential section is attached to the transmission case (or section), creating a substantial possibility of misalignment that will affect reliability and (b) that the design of the Audi transaxle creates a tendency for gear oil and transmission fluid to mix.